The present invention pertains primarily to a filter unit particularly adapted to remove moisture such as oil and water vapors contained in gases, such as air, when such gases are compressed by conventional compressors which inherently produce compressed gases which include at least a limited amount of oil and water vapors. Under circumstances where compressed gases such as air which are free from such vapors are required, it is necessary to remove the same by filtering and it is preferred that such filtering occur while the gases are under pressure, particularly where the gases are to be used in circumstances requiring that they have a pre-determined pressure, especially to operate certain instruments or mechanisms in which oil and water vapors cannot be tolerated.
It is possible to filter such compressed gases to remove oil and water vapors therefrom by employing one or a series of cartridges in a suitable container or housing having for example an inlet at one end and an outlet at the other end. Said cartridges contain desiccant material which, because of the relatively compact nature of the material, inherently impede the speed at which the gases can pass through the filtering cartridges. Such operation also is attended by a substantial decrease in pressure at the discharge end of the filter unit.
One example of a filter unit of the type referred to above is disclosed in U.S. Pat. No. 3,681,899, in the name of George A Grote, the instant applicant. Also, the filter shown in said patent is an in-line type of filter and the casing within which the filter cartridge or cartridges are mounted for operation is of separable, two-part construction. In order to separate one part from the other however, to either remove or replace cartridges therein, it is necessary to disconnect the line from the end of the part of the casing which is removed from the other part. Further, in the event more than one cartridge is included in the casing, the gas to be filtered must pass end-to-end through all of said cartridges.
Further, one of the characteristics of said aforementioned U.S. Pat. No. 3,681,899 is that it includes a transparent case which permits inspection of the condition of the cartridge unit therein to determine when replacement thereof is necessary. This is due to the fact that as oil vapor in particular is filtered from the gases by said unit, it progressively becomes darker in color and an experienced operator can determine from visual inspection when such replacement is necessary.
Efforts to improve the speed at which filtering of gases can be undertaken have occurred and one example of this is illustrated in several embodiments in U.S. Pat. No. 3,464,186, in the name of P. M. Hankison et al, dated Sept. 2, 1969. Relatively coarse filter material for condensing oil vapor, for example, is used in a vertical arrangement wherein desiccant type filter means is mounted above said coarse filter material for purposes of removing water vapor from the gases, the filtered gas discharging from the upper end of said vertical arrangement. Porous foam discs are disposed at opposite ends of said desiccant filter means and this entire arrangement imposes a distinct retarding effect on the speed at which gases pass through the entire assembly incident to being filtered.
Another embodiment of said Hankison et al patent discloses a coaxial arrangement of the coarse steel wire mesh filter which is disposed around the inner desiccant type filter, these filtering means being inclosed within non-transparent metallic tubular members. The direction of gases is such that they enter the lower end of the outer housing, passing upwardly through the coarse filter material to condense oil from the gases, the gases then extending upwardly and then being inverted to pass downwardly through the interior desiccant type filter means, the filtered gases discharging from the bottom of the unit. In order to clear the unit of accumulated condensate however, certain regeneration operations are required and, as in regard to the previously described embodiment of said patent, porous foam discs extend across opposite ends of the desiccant type filter means, whereby speed of operation of the filtering process and also minimizing reduction in the pressure of the filtered gases do not appear to be objectives of the patent. Further, if condensate is to drain by gravity from the coarse filter, it must flow downwardly in a manner to further saturate rising gases to be filtered.